My kid has two different cars: the black Audi TT that Costco sold a couple of years ago and the yellow Safety 1st Corvette. Both have been modified.

The Audi has been upgraded to 12v (two 6v batteries) and has a 2nd drive motor. The Corvette has the board removed and the battery is wired through the pedal to the motors. All the batteries seem to be in good shape and are relatively new.

Both cars have the same problem: they won't go uphill very long without stopping intermittently. It's like my kid has taken her foot off the pedal. They go fine on flat or downhill. This only happens uphill. Not sure if it's a current problem, motors overheating, or something else. The Audi has the same issue whether the 2nd drive motor is installed or not. This is a curious and frustrating issue.

Wondering if I could trying replacing the standard batteries with a pack of Li-Ion 18650. Pretty easy to get this close to 12 or 18v, and could add as many as needed for duration. Any reason this doesn't work well?

If your using an original battery, they have them built into the battery "package". The actual battery is inside the enclosure. If that's what your using, you can look on youtube on taking it apart to get the wiring harness for using an aftermarket battery.

Nope. Replacement battery and no enclosure. Based on the behavior is has to be in there somewhere. Worst case I can rewire from the battery to the pedal and see if that bypasses it. If not, then it must be a pedal issue.

Thanks for the help. Connection to pedal couldn't be simpler: Positive to pedal, then to motors. Neg direct to motors, plus a line back to pedal for braking. I removed the dash just in case there was something hidden where battery leads run. Nothing there.

Gotta be the pedal switch. Tiny chance it's a bad connector somewhere, so will replace them just to be sure. Unless I'm blind and missing something. Sure behaves like a thermal breaker, but I can't find anything.

I'd check all your connnections, plugs inside your shifters, I've found a lot of dirt and moisture inside the housing that had to be cleaned out, unplugged the 6 terminals one at a time and cleaned them then applied electrical grease, I found several of these terminals rusty from laying in this wet dirt. The pedal wiring is pretty straight-forward, I always apply electrical grease on every wire connection I take loose, whether its rusty or not. I've always pulled the breakers out and replaced w/inline 30amp auto fuses on the battery. Do you have a circuit board that controls the voltages to relays? The pedal sw usually either works or not, nothing more than a momentary contact sw.

Thanks again. To answer your questions... no more circuit board. It died a long time ago. For now, the shifter is not in the path. It's battery pos to the pedal, battery neg to the motors. Very little to go wrong here. Put my tester on the pedal and realized that the normally open circuit is not working (3 connections on the pedal switch - one for power, one normally closed, one normally open.) Can't get current through the normally open. So I have power to the motors through the pedal but no brakes (via motor shorting). So the pedal switch is clearly failing and I need a new one.

But back to drive train power issue, I can't recreate it in the garage. When I secure the car and run the motors I can't get them to stop. So it's either physical vibration from driving on the sidewalk that is breaking a connection or my kid is taking her foot off the pedal just enough to stop it. I don't see her moving her foot, but she's not quite tall enough for this car, so maybe.

Either way I need a new foot switch. May look at going with a true accelerator if one exists that will fit. Not sure something with a potentiometer that can handle the amps I need + an open connection in the off position can be found. For now just a working replacement foot switch would be fine.